The manner in which the belief is expressed is likely more important than the belief itself, especially if the belief itself is...uncommonly true. “I went to an elite Special Forces school,” “I’m going to die in six months,” “The FBI is following me,” “my father is trying to kill me,” are all true for some people, but expressing them with inappropriate affect or in circumstances where those beliefs seem doubtful or irrelevant might make you seem deluded. Scott Alexander wrote about this...

"The Soviet Union is politically dysfunctional"

Excessive worry about being diagnosed with a mental illness. Failure to distinguish "diagnosed with a mental illness" from "severely impacted by incarceration or other harassment due to such diagnosis". These things can be real problems, and you should seek help, rather than waiting for it to come to you.

Believing you're likely in a simulation

• data point: https://www.youtube.com/watch?v=sIt-w8BwvV4 (see description as well)

Various lifestyles: believing that polyamory can be an healthy relationship structure; believing practicing various kinks and sexual interests can be healthy